1. Field of the Invention
The present invention relates to a color CRT, and more particularly, to an inner shield of a color CRT that is capable of improving a shielding effect by enhancing a structure of an inner shield and capable of preventing a color spread phenomenon due to color mixture when an image is reproduced by reducing a variation degree in landing of an electron beam according to an external magnetic field variation according to the improved shielding effect.
2. Description of the Background Art
FIG. 1 is a partially-cut side view showing an internal construction of a color CRT having an inner shield in accordance with a conventional art, and FIGS. 2A and 2B are a rear view and a plan view showing the inner shield in accordance with the conventional art.
As shown in FIG. 1, a color CRT is formed with its external appearance by a panel 10 coated with a red, green and blue color fluorescent material 11 on the inner face thereof, and a funnel 20 sealed at the rear side of the panel 10 by a frit glass and maintaining an internal pressure in a high vacuum state of about 10-7 Torr.
A shadow mask 40 having fine slits serving for color selection is mounted at the inner side of the panel 10 through the medium of a frame 30, and the frame 30 is supported at the inner face of the panel 10 by means of the spring 50.
An inner shield 60 for shielding a magnetic field such as an earth magnetic field so that an electron beam 71 injected from an electron gun 80 is not influenced by the magnetic field is mounted at a rear side of the frame 30.
A neck portion 70 is installed at a rear side of the funnel 20, and the electron gun 80 for injecting the electron beam 71 is mounted at an inner side of the neck portion 70.
A deflection yoke 90 for deflecting the electron beam 71 injected from the electron gun 80 to the entire fluorescent surface coated with the fluorescent material 11 is mounted at a boundary portion positioned between the rear side of the funnel 20 and the neck portion 70.
Reference numeral 25 denotes a safety band for reinforcing the coupling portion of the panel 10 and the funnel 20.
Accordingly, when the electron gun 80 irradiates the electron beam 71, the electron beam 71 passes through holes 41 formed at the shadow mask 40 and collides with the fluorescent material 11 formed at the inner surface of the panel 10, radiating the fluorescent material 11, and according, an image is reproduced through the panel 10.
Especially, the inner shield 60 includes a vertical portion 62 extended in parallel to a tube central axis (X) and a slope portion 63 integrally formed at the rear portion of the vertical portion 62 and extended to be sloped toward the tube central axis (X).
As shown in FIG. 1, a front opening (Bf) is formed in front of the vertical portion 62, and a bent portion is formed bent vertically to the vertical portion 62 so that the inner shield 60 can be fixed with a clip (C) to the frame 30.
A rear opening (Br) relatively smaller than the front opening (Bf) is formed at a rear side of the slope portion 63.
The inner shield 60 of a color CRT of the conventional art, however, has several problems.
That is, for example, with reference to FIG. 2B, since the height (h1) of the vertical portion 62 is too small for the entire height (H) of the inner shield 60 constituted by the vertical portion 62 and the slope portion 63, the slope portion 63 is away from the funnel 20 with the big distance (d) therebetween, resulting in that efficiency in shielding the earth magnetic field is degraded.
In case where the inner shield 60 is adopted to a product of a color CRT and used for some periods, since the shielding efficiency of the earth magnetic field is degraded, the variation degree that the electron beam is landed becomes great according to the variation of an external magnetic field, causing a problem of occurrence of a color spread due to a color mixture when an image is reproduced.
When the color spread occurs due to such factors, the product of the color is CRT purchasing a high image quality is devaluated, and a reliability of the product is accordingly degraded.
Therefore, an object of the present invention is to provide an inner shield of a color CRT that is capable of improving a shielding effect by enhancing a structure of an inner shield and capable of preventing a color spread phenomenon due to color mixture when an image is reproduced by reducing a variation degree in landing of an electron beam according to an external magnetic field variation according to the improved shielding effect.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a color CRT having an inner shield being mounted at a frame inside a panel and a funnel to shield an earth magnetic field, the inner shield having a vertical portion formed in parallel to the central axis of the CRT and mounted at the frame, a slope portion extended slanted against the central axis of the CRT at a rear side of the vertical portion and a notch with its central portion formed concave at the end portion of the slope portion, the opposite of the frame, and under the assumption that the entire height of the inner shield constructed with the vertical portion and the slope portion is xe2x80x98Vxe2x80x99, a height (V1) of the vertical portion satisfies the relational expression of 0.18xe2x89xa6V1/Vxe2x89xa60.25, and on the assumption that the shortest height from a starting point of the vertical portion to the notch is V2, the height V1 of the vertical portion satisfies a relational expression of 0.40xe2x89xa6V1/V2xe2x89xa60.54.
On the assumption that a sectional area of a front opening formed by the vertical portion, the frame side, is xe2x80x98Afxe2x80x99 and a sectional area of a rear opening formed by the slope portion, the opposite side of the frame, is xe2x80x98Arxe2x80x99, the inner shield is designed to satisfy a relational expression of 0.56xe2x89xa6Ar/Afxe2x89xa60.78.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.